Soviet President Leonid Brezhnev has sent personal messages to the leaders of NATO countries in a major diplomatic drive to block deployment of new U.S. medium-range nuclear missiles in Western Europe.

Government officials in West Germany, Britain, the Netherlands, Norway and Denmark confirmed that the message had been hand-delivered to their heads of state by the Soviet ambassadors in their capitals between Saturday and today.

In some meetings, the Soviet envoys also explained and amplified the written messages which restated Brezhnev's offer to reduce Soviet troops, tanks and nuclear missiles in Eastern Europe if NATO abandons plans to modernize its nuclear missiles in Western Europe.

It was put "into the format of a personal letter," one source said. Brezhnev said in a speech at the 30th anniversary of East Germany that the Soviet Union would withdraw unilaterally 20,000 troops and 1,000 tanks from East Germany, where Moscow now maintains 400,000 troops and 7,000 tanks. He also offered to reduce the number of nuclear missiles aimed at Western Europe if Nato would give up its plan to deploy the new U.S. Pershing II and Tomahawk Cruise missiles in Western Europe.

While Brezhnev sought to discourage NATO from modernizing its nuclear forces, Danish sources stressed that their country and seveal other NATO allies were also looking at his statement for signs of serious Soviet desires for reduction of nuclear forces by both sides.

Brezhnev's speech also threatened "stern" Soviet countermeasures if NATO went ahead and deployed the new missiles in West Germany and neighboring countries. He implied that if countries like the Netherlands or Belgium allowed the new NATO missiles to be deployed at U.S. bases on their territory, as both the United States and West Germany desire, they may be made target of Soviet nuclear weapons.

In Bonn, sources close to Chancellor Helmut Schmidt said today that the tone of Brezhnev's personal message to Schmidt, which was hand-delivered on Saturday before Schmidt left for a visit to Ireland, was more moderate than Brezhnev's East Berlin speech.

While his speech was regarded in many European capitals as somewhat harsh in tone, the sources said, Brezhnev's message to Schmidt was "more courteous and diplomatic" and communicated his argument "on a personal basis at the highest levels."

But the sources in West Germany, and in Norway and the Netherlands, where the message was received today, said it contained no new details of Brezhnev's East Berlin offer and failed to answer questions that have failed to answer questions that have been raised since about whether the Soviet Union really was interested in mutual reduction of forces in Europe.

[In Moscow, Brezhnev did not attend two scheduled meetings and a banquet with Syrian President Hafez Assad Monday and Tuesday, the Associated Press reported. It quoted Syrian sources as saying that the Soviet leader was ill. Western diplomats raised the possiblity of a "diplomatic illness," a malady preventing him from having to respond to Assad's reported demands for Soviet weapons.]

In London, Soviet Ambassador Nikolai Lunkov met for half an hour late yesterday afternoon with British Prime Minister Margaret Thatcher to deliver and explain Brezhnev's message. Thatcher made no reply, according to sources there, except to agree to "take note" of the message and Lunkov's explanation.

In a major speech at her Conservative Party's annual convention last week, Thatcher had warned that "we must expect to see the Soviet Union mount a powerful psychological campaign" to prevent NATO from correcting a growing imbalance of power in Europe by modernizing its nuclear forces with medium-range missiles to match Moscow's.

She told the convention delegates she would study Brezhnev's East Berlin speech "to see whether it is the opening shot in such a campaign or whether it is a genuine attempt to reduce tension in Europe."

But she also laid the ground for British approval for the modernization of NATO's nuclear weapons in Europe by detailing the Soviet arms buildup, expressing "alarm" at the number of "Soviet nuclear weapons targeted on Western Europe" and repeating her belief that "the threat to European freedom is greater now than at any time since 1945."

British and U.S. officials reportedly have already agreed to five U.S.

military stations, mostly in Eastern England, where ground-based Cruise missiles, with a range of more than 1,000 miles, will be based.

The defense ministers of NATO nations are to decide in December whether to deploy 464 Cruise missiles and 108 Pershing missiles in West Germany and possibly Holland, Belgium and Italy. NATO now has an estimated 9,000 nuclear warheads of various kinds in Europe, where there have been nuclear weapons for nearly 30 years. However, West Germany wants other European NATO nations, excluding an existing power like Britain, to accept some of the new missiles.

Scandinavia's NATO members, Norway and Denmark, do not allow nuclear weapons of any kind on their soil, and the Netherlands and Belgium are considered to be undecided on new NATO missiles.

A Belgian official said last night he did not think his government had yet received Brezhnev's message. Dutch officials said they had received it but that it was so similar to Brezhnev's East Berlin speech it did not change anhthing.

They reiterated that the Dutch government would not even consider allowing any of the new missiles onto U.S. bases there until and unless the U.S. Senate ratified the SALT II nuclear arms limitation agreement between the United States and the Soviet Union. Dutch sources had said earlier that the government saw Brezhnev's speech as an obvious effort to stir up leftist and already stron antinuclear sentiment in the Netherlands.

Sources here in Denmark compared Brezhnev's speech and message to the Soviet Union's campaign to discourage Europea NATO countires from deploying an American neutron bomb. But the impact of Brezhnev's new campaign will be different here, one senior government source said.

"People figure in this case that if the Russians have medium-range missiles aimed at us, why shouldn't NATO have the same thing," the source said. "The neutron bomb was to be a brand-new weapon that the Russians said they didn't have."

Although it will not change its policy about keeping nuclear weapons off its soil, Denmark is likely to approve the NATO nuclear modernization.

Denmark and Norway are particularly concerned about Soviet military buildups at bases in the nearby Soviet northwest along the Artic Ocean and Baltic Sea, whose sea lanes to the North Atlantic pass by the Scandinavian NATO nations. Soviet naval and aerial maneuvers in recent years have passed increasingly close to Denmark and Norway, which both are improving their preparedness for the landing of NATO reinforcements for their own military forces in the event of a Soviet attack.